The present apparatus and method relates to spray coating sheet materials and, more particularly, to an apparatus and method for spray coating sheet material with a heated and atomized liquid compound to decrease coating drying time, improve coating quality and increase production efficiency.
Application of spray coatings to sheet materials, such as forming lubricants sprayed onto sheet metal or coiled steel, that undergo drawing operations exposing the sheet and lubricant to extreme pressures are known in the art. The application of lubricants suitable for sheet metals varies on the forming process used, material to be coated and the properties of the lubricant itself. It has long been known to apply common oils and greases to lubricate the sheet to facilitate drawing or forming and to prevent unwanted thinning or tearing of the material. In the case of ferrous materials, the greases and oils further acted to prevent premature corrosion. These common greases or oils, however, were difficult to remove since such solvents required special handling and storage.
During World War II, oils and greases became difficult to obtain, and it was discovered that borax or soap-based lubricants provided the necessary lubrication without having to remove the lubricant prior to subsequent coating of the sheet material with primer or paint. Such soap-based lubricants were dissolvable in water, rolled or sprayed on the sheet material, and eventually dried on the sheet once the water evaporated. The soap-based lubricants, although applied mixed with water, became known as xe2x80x9cdryxe2x80x9d lubricants as the lubricant is dry at the time of forming the sheet metal. Progression of the sheet metal along the processing line was dependent on the typically lengthy drying time of the lubricant which required reduced line speeds. Due to the need to keep the process line moving, a significant length of floor space was needed to ensure drying of the lubricant prior to further processing.
Prior methods for applying dry lubricants were typically conducted by spraying an excessive amount of a lubricant/water mixture onto the sheet material. In order to obtain the recommended or desired coating weight per square foot of material, prior roll coating processes used rubber rollers on the top and bottom surfaces of the sheet metal to squeeze or press the undesired quantity and weight of the sprayed-on lubricant from the sheet material. Such prior art processes provided full coverage of the sheet metal but had numerous disadvantages.
The prior roll coating processes are problematic in that dry lubricants are very costly, and the prior art methods used excessive amounts of dry lubricant, much of which was wasted through the spraying and squeezing process and often producing uneven coating weight on the material. The prior art processes were further problematic in that the rubber rollers used to squeeze off excess lubricant were subject to wear requiring reconditioning or replacement and added to uneven coating weight of the dry lubricant. The prior art processes were further problematic in that they slowed the process line speed requiring significant space in the process line and time for the water to sufficiently evaporate from the sheet material. The prior art processes were further subject to significant down time of the process line due to replacement of worn rollers and the necessity to change the rollers between coating production runs.
Consequently, it would be desirable to provide a spray coating apparatus and method that improved the problematic conditions in the prior art, that is efficient in applying a desired coating weight, that improves the consistency of the coating, that reduces clogging of the apparatus, that facilitates an increase in productivity through an increase in process line speed, that reduces the space required for the apparatus in the process line and space needed for drying the coating, and that is simple and relatively inexpensive to produce and operate.
The spray coating apparatus of the present invention includes a base having a batch tank positioned thereon which is used to contain and mix water with a water soluble material to form a liquid compound. The apparatus includes at least one spray control valve in fluid communication with the batch tank to selectively dispense the liquid compound from the batch tank to at least one spray nozzle. The apparatus further includes at least one spray nozzle which is adapted to receive the liquid compound from the control valve and receive a supply of heated gas which is mixed with the liquid compound in the nozzle to heat and begin atomizing the compound and spray the atomized compound onto the sheet material.
In another embodiment of the invention, the apparatus further includes a spray header positioned along the coating line for the sheet material in spaced relation to the base. The spray header includes a plurality of spray nozzles adapted to receive and communicate with the liquid compound and the heated gas.
In another embodiment of the invention, steam is used as the heated gas that is placed in communication with the liquid compound.
In yet another embodiment of the invention, a process tank is positioned on the base in fluid communication with the batch tank to hold a reserve of mixed liquid lubrication compound to be sent to the spray control valve.
In an additional embodiment, a user control terminal is positioned on the base for monitoring and controlling the mixing of the liquid lubrication compound and the spraying of the atomized lubricant on the sheet material.
The present invention also provides a method for applying a spray coating to sheet material including the steps of adding a water soluble material to a quantity of water in a batch tank and mixing the material with water in the batch tank to form a liquid compound. The liquid compound is selectively dispensed under pressure to at least one spray nozzle. The liquid compound is then atomized and sprayed onto the sheet material traveling along a coating line.
In another embodiment of the inventive method, the water and liquid compound in the batch tank are heated in the batch tank.
In another embodiment, the spray nozzles are adapted to receive and communicate the liquid compound and a heated gas to further heat the liquid compound and begin atomizing the liquid compound.
In yet another embodiment of the inventive method, a process tank is provided in fluid communication with the batch tank to store a reserve of liquid lubrication compound to be selectively dispensed to the spray nozzle.
In an additional embodiment of the inventive method, a plurality of spray control valves and spray nozzles are provided for dispensing the liquid lubrication compound through selected valves to selected nozzles to coat the material sheet.
In even another embodiment of the inventive method, a heated gas is supplied to a jacket in the spray nozzle to heat and deter clogging of the nozzle.
In a further embodiment of the inventive method, a user control terminal is provided to control and monitor the mixing and spraying of the atomized lubrication compound to the sheet material along the coating line.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.